DEGRADATION OF REGOLITH SURFACES IN THE ANNUAL AND 100 KYR TIME SCALES, MONO BASIN, CA

The degradation of the Earth’s surface is ubiquitous. Among other things it affects the preservation of geological features, landforms, remains of past life forms, artifacts, and manmade structures. The importance of the landscape evolution is dictated by the rates; how fast the erosion operates, how fast the regolith is transported, and how fast is the rate of deposition. The long term averages of degradation are relatively well known in the landscape wide scale; scale of kilometers or tens of kilometers. However, the degradation at a landform scale is poorly understood; the scale of meters to tens of meters.

Our research is concentrated on the landform scale degradation in annual to tens of thousands of years temporal scale. Much of our research is done on the tall moraines flanking the Sawmill and Bloody Canyons in the Mono Basin, CA. We have studied the long term degradation by comparing the topographies, the changes in the shape and steepness, of young (recently formed) moraines to old (tens of thousands of years old) moraines. Based on comparative analyses of the landforms such as lateral moraines, lakeside bluffs, and cinder cones it is apparent that the moraines have degraded for 10’s of meters over their lifespan of 10’s of thousands of years. The significant degradation is also supported by the analyses of the cosmogenic boulder ages from the crests of these moraines that show a large variation in ages. The age variation is consistent with gradual exposure of boulders as the regolith degrades over time. We have also documented and modeled the frequency of surface boulders which decreases towards the flanks of the moraines. This is also consistent with significant degradation, as the boulders are continuously unearthed at the crest and buried on the flanks.

We are currently studying the short term/annual degradation by tracking the mobility of the surficial sediments. This is done, among other methods, with soil traps, repeat photography, and transport markers. We will present the results of both long term (~100 kyrs) and short term (1-~100 yrs) degradation and contrast the rates of degradation at these two very different temporal scales.